The Commerce Commission has opened investigations into both Cook Strait ferry companies after months of cancelled and delayed sailings.
The investigations into KiwiRail, which owns Interislander, and StraitNZ, which owns Bluebridge, are in the early stages, according to Vanessa Horne, the commission's general manager for fair trading.
They needed to consider whether consumers have been accurately informed of their rights to a refund or getting costs covered under the Consumer Guarantees Act when ferry sailings were disrupted and people were forced to make other arrangements.
She said the maximum penalty for a business found in breach of this part of the act was $600,000.
Jon Duffy, chief executive of Consumer NZ, said he was pleased their complaint had been picked up.
"Under the Consumer Guarantees Act, businesses that are providing services to consumers have to exercise reasonable care and skill when they provide those services to the customer, and if they don't, the customers have remedies.
"If ferries are regularly being cancelled because of mechanical failure, there's a really strong argument that the ferry operators are not exercising reasonable care and skill in putting serviceable vessels into service."
He said it was not fair for passengers to shoulder expenses when dealing with a cancelled sailing - like accommodation, parking costs, or flights - and the Consumer Guarantees Act agreed.
The terms and conditions of both ferry companies carry clauses denying responsibility for these costs.
Yet Bluebridge confirmed it was working with customers on a case-by-case basis to reimburse them. A number of payments had been completed already, but it didn't say how many.
Duffy said this clause went against the act.
"What we've alleged in this is that the ferry companies are actually misleading passengers about their rights because they're actually telling them that they don't have any rights to have those expenses covered.
"They need to stop actively saying that they're not liable for those costs, because that's what their terms and versions are saying."
He said it was concerning that New Zealanders might be out of pocket for thousands of dollars which they could have claimed back over the years.
"It's just that this issue was going under the radar because the volume of complaints was too low and agencies weren't looking into it."
Repercussions for the ferry companies could range from a scolding, to fines, to criminal charges.
Interislander executive general manager Walter Rushbrook confirmed they had been advised of the inquiry by the commission.
He said they would be cooperating fully, and "we remain confident we have complied with our obligations under the Fair Trading Act".